There are many preamplifiers known from the state of the art and designed for a wide variety of applications. One special problem using preamplifiers occurs in cases in which the signal voltage to be amplified comes from a signal source with high or very high source impedance. For example, it can be found that when transmitting relatively low-frequency signals via low coupling capacity on conventional operational amplifiers frequently used as preamplifiers and connected as voltage sequencers with high leakage resistance, high signal losses occur. These signal losses are, naturally, unwanted.
A second teaching of the invention concerns a preamplifier for amplifying signal voltages from a signal source with high source impedance with a signal input connected to the signal source and a signal output supplying an output signal.
When preamplifiers are used to amplify signal voltages from a signal source with high source impedance, it is known to be a problem that, because of the high to very high source impedance, the signal voltage is very sensitive to outside electrical fields. Such outside electrical fields can cause high signal losses even before the preamplifier.